1-27-25 Prokaryotic Transcription

Transcription direction: RNA synthesis occurs from 5′ to 3′ while the template DNA runs from 3′ to 5′.
Coding (nontemplate) Strand: The strand of DNA that shares the same sequence as the resulting mRNA and corresponds to the amino acid sequence of the protein produced.
RNA Polymerase: An enzyme responsible for synthesizing RNA using a DNA template; this enzyme is formally known as DNA-dependent RNA polymerase.

Promoter: A DNA sequence where RNA polymerase initiates transcription.
Start Point: The first DNA base included in the RNA sequence.
Terminator: A sequence that signals RNA polymerase to stop transcription.
Transcription Unit: The DNA sequence that is transcribed into RNA, bounded by the start and termination points.
Upstream/Downstream: Referring to DNA sequences that are located in the opposite direction from or procedural to the expression from the transcription site.
Primary Transcript: The unprocessed RNA transcript corresponding to a transcription unit.

Transcription Bubble: RNA polymerase creates a transient separation of DNA strands, forming a "bubble" that facilitates RNA synthesis.
Stages: The transcription reaction consists of three stages: initiation (formation of a closed complex at the promoter), elongation (RNA chain elongation in a 5′ to 3′ direction), and termination (dissociation of RNA polymerase at terminator sites).

Holoenzyme: The functional form of RNA polymerase, composed of the core enzyme (five subunits) and a sigma factor.
Subunit composition: Core enzyme is a multisubunit complex approximately 400 kD, with essential catalytic functions located mainly in the β and β′ subunits.

Promoter Recognition: RNA polymerase binds to DNA randomly and exchanges between potential sites until it locates a promoter.
Initiation Process: RNA polymerase must separate DNA strands and provide nucleotides for RNA synthesis while overcoming the initiation complex.

Promoter Specificity: The sigma factor enhances RNA polymerase's capacity to bind to specific DNA sequences (promoters) and is often released once RNA reaches about 10 bases.
Conserved Sequences in Promoters: Short consensus sequences provide binding regions for sigma factors, generally including regions like the TATA box (−10 element) and the −35 element.

Classification of Mutations: Mutations either reduce or increase promoter efficiency by altering sequences near the consensus, influencing binding properties and the melting reaction to open complexes.

Footprinting Technique: Used to discover protein-DNA interactions by marking protected regions on DNA against nuclease activity.

Enzyme Movement: RNA polymerase experiences conformational changes that facilitate nucleotide entry to the active site, utilizing a Brownian ratchet mechanism to progress the polymerization.

Intrinsic Terminators: Sequences recognized directly by RNA polymerase leading to transcription termination via formation of a hairpin structure in the RNA.
Rho-dependent Terminators: Require the Rho protein to terminate transcription by interacting with the RNA transcript.

Function of Rho Factor: Rho binds to the nascent RNA and tracks to release RNA polymerase from elongation complexes at terminator sites.

Regulatory Dynamics: Bacterial sigma factors undergo complex regulatory mechanisms affecting stress responses, with examples such as the heat-shock response that targets denatured proteins.

Sporulation Process: Controls the transition of bacterial cells to spores during environmental distress, with a necessary sequence of sigma factor changes to ensure proper timing and development.

Antitermination Complexes: Allow RNA polymerase to bypass terminators, crucial in regulating transcription for both early and late phage genes under varying conditions.